Chairs having one-piece seat-and-back supports are known. For example, St. John U.S. Pat. No. 293,813, issued Feb. 19, 1884, discloses a chair comprising an elongated seat-and-back support mounted on a floor-engaging base. The seat-and-back support comprises a lower, rigid, U-shaped seat support and an upper relatively resilient back support extending upwardly from the seat support. When a rearward and downward force is exerted on the seat-and-back support, the upper back support deflects backwardly and downwardly.
Although the back support of St. John's seat-and-back support is flexible, the seat support thereof is not. Thus, while the back support is designed to deflect downwardly and backwardly relative to the seat support in response to an occupant's weight, the seat support is not so constructed. Such design has been determined to be insufficient in providing the necessary comfort for users, especially in work environments where the chairs are occupied for extended periods of time.
It has thus been found desirable to provide a chair one-piece seat-and-back support comprising a U-shaped seat support with upper and lower leg portions and an intermediate bight portion, and a back support with a lower bight portion and an upright back portion, wherein both bight portions are flexible thereby enabling the seat support and the back support to adjustably respond at different rates of deflection to an occupant's weight. This chair design has been determined to be most adequate in providing the necessary comfort to the chair occupant.
It has also been found desirable to provide a resilient stiffening means, such a leaf spring, between the upper and lower leg portions of the seat support to strengthen the same and increase resistance to relative deflection of the upper leg portion of the seat support.
It should be noted that the use of leaf springs in chairs to resist tilting of seat supports are known, although such biasing means have not been used in chairs of the preferred type heretofore described. For example, Benzing U.S. Pat. No. 3,337,265, issued Mar. 4, 1965, discloses a chair comprising, in relevant part, a pair of inverted U-shaped sides connected by a pair of transverse and longitudinal horizontal supports. A pair of U-shaped springs are mounted on the transverse supports. A substantially L-shaped seat-and-back support is mounted on top of the springs. In this manner, when a rearward and downward force is exerted on the seat-and-back support, same reclines downwardly and backwardly against the tension of the springs.
In addition, Werner U.S. Pat. No. 3,740,792, issued June 26, 1973, discloses a chair comprises a box-like lower housing open at back and top portions thereof and mounted on top of a pedestal. An upper seat support is pivotally mounted to the housing on a horizontal shaft. A number of overlapping leaf springs surround the shaft and engage the housing and the seat support. The springs bias the seat support in a horizontal position. When a downward force is exerted on the seat support, the same pivots against the tension of the springs.
Benzing also provides for adjustment of the leaf springs' resistance to deflection of the seat support relative to the housing. Specifically, the tension of the springs is adjusted by turning a lever which displaces the springs forwardly and rearwardly toward and away from the pivotal axis of the seat support to increase the moment arm of the springs and thus vary the tension of the same.
In contrast to the leaf spring tension adjustment means disclosed by Benzing, it has been found desirable to provide tension adjustment means in a chair having a one-piece seat-and-back support, wherein the adjustment means adjustably engages the leaf spring along a longitudinal axis thereof to increase and decrease the effective length of the spring to thereby decrease and increase, respectively, the spring's resistance to deflection of the seat support.